我正在实施代码,以便在this algorithm之后的给定BST(binary search tree)
中构建post-order traversal array
。我没有回到binary Search Tree
。我得到的东西毫无意义。这是我的代码
public class BinaryTreemethods {
public static void main(String[] args) {
int[] preOrder = { 5, 3, 1, 4, 8, 6, 9 };
int[] inOrder = { 1, 3, 4, 5, 6, 8, 9 };
int[] postOrder = {1,4,3,8,6,9,5};
static int postIndex=postOrder.length-1;
Node postordertree= buildBinarytreefromPostOrder(postOrder, 0, postOrder.length-1);
System.out.println("pre order traversal of node from postorder reconstructed tree ");
printPreOrder(postordertree);
}
private static void printPreOrder(Node tree) {
if (tree != null) {
System.out.print(" " + tree.data);
printPreOrder(tree.left);
printPreOrder(tree.right);
}
}
//this just reconstructs BT from post-order traversal elements
public static Node buildBinarytreefromPostOrder(int[] post, int start, int end){
if (postIndex<start || start > end ){
return null;
}
Node root = new Node(post[postIndex]);
postIndex--;
if (end == start){
//System.out.println("called");
return root;
}
int i = 0;
for (i=end;i>=start;i--){
if (post[i]<root.data)
break;
}
// Use the index of element found in postorder to divide postorder array
// in two parts. Left subtree and right subtree
root.right=buildBinarytreefromPostOrder(post,i+1, postIndex);
root.left=buildBinarytreefromPostOrder(post,start,i);
//root.left=buildBinarytreefromPostOrder(post,start,i);
//root.right=buildBinarytreefromPostOrder(post,i+1, postIndex);
return root;
}
}
我在pre-order traversal is 5 9 6 8 3 4
中打印时输出不正确。
我知道哪里出错了?
编辑:交换root.right and root.left
的行顺序后(注释掉之前的行),
left tree
构建正确,但右树不是。我得到的输出是
5 3 1 4 9 6 8
答案 0 :(得分:2)
作为每个子树的根,你正在使用postIndex
,这是整个结构的全局。你应该采用子阵列的最后一个元素(end
)。
应该是这样的
public static Node buildBinarytreefromPostOrder(int[] post, int start, int end)
{
if (end < start)
return null;
Node root = new Node(post[end]);
if (end == start)
return root;
int i;
for (i = end; i >= start; i--)
if (post[i] < root.data)
break;
root.left = buildBinarytreefromPostOrder(post, start, i);
root.right = buildBinarytreefromPostOrder(post, i + 1, end - 1);
return root;
}